1. Field of the Invention
The present invention relates to a semiconductor device.
2. Description of the Related Art
One kind of semiconductor device for focus detection includes a pair of sensor units. Upon detecting that the output of one sensor unit to be used for detection has reached a predetermined value, processing of the focus detection signal of the other sensor unit to be used for signal is controlled. More specifically, each of the pair of sensor units includes photoelectric conversion units. This semiconductor device controls the accumulation operation of charges generated by the photoelectric conversion units of the sensor unit for signal in accordance with the signal corresponding to charges generated by the photoelectric conversion units of the sensor unit for detection. The charge accumulation operation is controlled by, for example, controlling the charge accumulation time or the accumulated charge amount. More specifically, when the object has a low luminance, the charge accumulation time is prolonged, or the accumulated charge amount is increased. When the object has a high luminance, the charge accumulation time is shortened, or the accumulated charge amount is decreased. This allows for control of the charge accumulation operation of the photoelectric conversion units of the sensor unit for signal.
After that, the signal corresponding to the charges accumulated in the sensor unit for signal can be output, as information for focus detection, to a calculation unit that executes a focus detection operation. Actually, each sensor unit can include about 30 to 80 photoelectric conversion units arranged in a line or in an array. Two pairs of sensor units are prepared, and focus detection is performed by a phase-difference detection method using two images formed by the sensor units.
Apart from the above-described series of focus detection operations, another focus detection operation may independently be performed using the signal corresponding to the charges generated by the sensor unit for detection as information for focus detection. This is expected to enable more accurate focus detection. However, when the control signal of the sensor unit for signal is switched, noise may mix in the signal of the sensor unit for detection. For example, crosstalk noise can mix in due to wiring capacitance coupling between signal wirings. Noise can also mix in when processing of the signal corresponding to the charges accumulated in the sensor unit for signal starts.